Method for calibrating a photofinishing system and components for use in such a method

ABSTRACT

An apparatus for calibrating a printer of a photofinishing system, comprising: 
     (a) a reference film strip carrying at least one reference image; 
     (b) a reference chart carrying multiple renderings of the reference image representing different printer exposures; and 
     (c) a substrate carrying printer correction factors needed to change a photographic print obtained from the reference image on the reference film strip, to match any desired rendering on the reference chart. A method of producing the above reference chart, and a method of calibrating a printer of a photofinishing system, are also provided.

FIELD OF THE INVENTION

The present invention relates in general to photofinishing systems andis particularly directed to a device (kit) and method which allowssimple calibration of a photofinishing system printer.

BACKGROUND OF THE INVENTION

Photofinishers customarily employ one or more quality control tools,typically in the form of either reference first or second generationoriginal developed negatives. "First generation" and "second generation"original negatives are described in U.S. Pat. Nos. 5,223,891 and5,313,251. These developed reference images frequently consist of humanportrait images and reference color or neutral gray patches.Photofinishers have typically calibrated their printers by printingthese developed negatives, measuring the densities of reference patcheson the resulting prints using a densitometer, and adjusting printercalibration controls until the densities of the reference patches reachrecommended (desired) values.

Originally, these reference images were camera originals (that is, firstgeneration originals) and were specified to extremely high standards.Because of these high standards, the production of them was timeconsuming, labor intensive and expensive. The adoption of secondgeneration originals as control tools (as disclosed in U.S. Pat. Nos.5,223,891 and 5,313,251), helped to address the above issues and alsofacilitated:

a. Identical images on multiple copies of a reference developed filmstrip.

b. Higher standards of sensitometric uniformity between multiple copiesof a reference developed film strip.

The calibration of printers using second generation originals was stillgenerally achieved by measuring the reflection densities of acalibration patch in the image and comparing those densities tospecified aim densities provided with the control tool. A less formalmethod of calibration involved repeatedly printing the image afteradjustment of the printer balance until a pleasing result, possiblymatching a single reference print, is obtained.

However, the previously used methods have a number of disadvantages.First, if the desired result is not obtained when the reference imagesare printed, there is no indication of how the printer should then beadjusted to obtain the desired result. Adjustments are usually made bytrial and error, the number of trials required depending on theexperience and color discrimination of the operator. Second, ifcalibration is achieved by visual matching to a supplied referenceprint, that reference print is the only available aim referenceavailable. This aim may not reflect the color balance or density desiredby the photofinisher. Third, if calibration is achieved by densitometricmeasurements of a calibration patch, while that patch can be adjustedperfectly there is a trade off in obtaining the desired rendering of thecalibration patch (such as a typical gray patch) compared to otherimportant colors in the scene. Fourth, because processed negatives wereused, this method of calibration failed to take account of any bias oroffset in the film processing components (that is, the physical andchemical components of the film developing process) between the filmprocess used by the calibration kit manufacturer to develop thereference film strip and the film processing components used by thephotofinisher to develop customer negatives from a customer film strip.

SUMMARY OF THE INVENTION

The present invention, then, provides an apparatus for calibrating aprinter of a photofinishing system, comprising:

(a) a reference film strip carrying at least one reference image;

(b) a reference chart carrying multiple renderings of the referenceimage representing different printer exposures; and

c) a substrate carrying printer correction factors needed to change aphotographic print obtained from the reference image on the referencefilm strip, to match any desired rendering on the reference chart.

The present invention further provides a method of making a referencechart useful in the above apparatus, and a method of calibrating aprinter of a photofinishing system using the apparatus.

The apparatus and method of the present invention can provide a numberof advantages. First, when a desired rendering is not obtained when thereference images are printed, the apparatus provides a quantitativeindication of how the printer should then be adjusted to obtain thedesired rendering. Second, a large number of different color balancesand density renderings can be available on the reference chart and thephotofinisher may select any one of these as his desired aim. Third,because calibration is primarily achieved by visually matching an idealcompromise between balance and density of all important elements in thereference scene can be more easily achieved. Fourth, because unprocessednegatives are used, the method of the present invention takes account ofany bias or offset in the film processing components of thephotofinisher.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a flowchart illustrating the method of the presentinvention used to prepare a reference chart;

FIG. 2 is a view of a reference chart produced by the method of FIGS. 1Aand 1B;

FIG. 2A is an enlarged view of a rendering on the chart of FIG. 2; and

FIG. 3 is a flowchart illustrating a kit of the present invention, and amethod of the present invention for calibrating a photofinishing systemusing such a kit.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

EMBODIMENTS OF THE INVENTION

Referring first to FIGS. 1A and 1B, a capture film, 102, on which theoriginal image, 110, of the scene, 108, is captured, is selected.Preferably the capture film 102 should have wide exposure latitude, highsharpness and good color rendition. This film is used to photograph thereference scene, 108. Additional exposures of the reference scene 108are also made with the inclusion of various diagnostic charts anddevices. Further analytical exposures are additionally produced on thecapture film using an exposing device such as a sensitometer, 104, toproduce undeveloped sensitometer exposure 106 on the same capture film102. Since each of the separate photographic and sensitometric exposureson the capture film is used in the determination of the tone and colorcharacteristics of the developed reference scene photograph, they aredeveloped together in a well controlled film processor, 112, in theconventional manner.

The developed reference scene photograph and diagnostic andsensitometric exposures, 114, are scanned using a digital film scanner,116. Optimum quality requires the use of a scanner having very highspatial resolution and stable color sensitivities. The resulting digitalimages, 118, are in a metric that is scanner dependent and will becalled scanner density in this discussion. Scanner density isrepresentative of the opto-electronic response of the scanner system tothe optical density modulation in the developed negatives.

The digital image data (files) resulting from scanning the diagnosticand analytical exposures are then numerically analyzed. The developednegatives of the sensitometric exposures are also measured usingappropriate integral densitometry. The data obtained is then used todetermine the capture film and scanner characteristics and therebyconstruct a digital data transform, 120, that removes the scannercharacteristics (such as spectral sensitivity) and the tone and colorreproduction characteristics of the capture film from the scannedreference image. The components of such a transform may include, butneed not be limited to, particular one-dimensional mapping operations,multi-dimensional lookup tables, matrix operations, interpolationoperations, sampling operations, clipping, shifting and scalingoperations, the uses of which are familiar to those skilled in the artof digital image processing or other types of data transformingoperations. The digital image, 122, resulting from application oftransform 120 is now a representation of the reference scene in terms ofexposure density into the three color records of the capture film.Exposure density is a logarithmic quantity representing the imagewisequantity of exposing light reaching each photosensitive record of thecapture film. Thus the digital image 122 in exposure density isindependent of the color and tone reproduction characteristics of thecapture film but is still dependent on the spectral sensitivities of thevarious photosensitive records of the capture film. That is, digitalimage 122 carries independent color signals corresponding to the signalssensed in each color channel of the capture film 102 (typically thesignals may be in the form of red, green and blue signals, correspondingto the signals sensed by the cyan, magenta and yellow sensitive recordsof film 102).

Digital image 122 can now be manipulated if desired to change certainimage characteristics or to add specific resolution targets or colorcalibration patches. This is accomplished using digital transform 124,leading to digital image 126, containing the (possibly modified)reference image with added resolution targets or color calibrationpatches.

If the product film type (the product film type being the type of filmfor which a calibration kit using the final reference chart, is beingdesigned), has a different spectral sensitivity in its photosensitiverecord(s) than capture film 102, then it is necessary to develop asecond transform, 128 which can transform the exposure densities assensed by the capture film into exposure densities that would have beensensed by the product film type, producing digital image 130. Spectralsensitivity measurements for the photosensitive recording layers of thecapture film 102 and the product film type are required to build thistransform. These spectral sensitivities can be obtained in a knownmanner.

Digital image 130 must now be transformed in a way that digitally modelsthe printing of a negative of the reference image on the product filmonto the product photographic paper (a selected type of photographicmedium), using a photofinishing system printer, to produce aphotographic print of preselected balance. This is accomplished usingdigital transform 132. The resulting digital image, 134, represents theexposures that would be recorded in each photosensitive layer of theproduct photographic paper at the time of printing, if the printer werecorrectly balanced and calibrated. The data required to constructtransform 132 include spectroscopy and integral densitometry readings ofa set of images of color patches on the product film, where the set ofcolor patches represents a reasonably uniform sampling of the colorgamut of the film, the power spectrum of the printer lamp and thespectral sensitivities of the various photosensitive layers of theproduct photographic paper.

Digital image 134 is the basis image from which the reference chart isconstructed. Steps 136 through 144 are repetitively applied to buildeach of the component images for the reference chart Digital transform136 models a photofinishing system printer exposure adjustment (whichincludes both chromaticity, that is color balance, adjustments, as wellas lightness adjustments), so that different exposure levels of theimage can be generated which can produce photographic prints on theselected medium (the product type photographic paper) of balances (bothcolor and lightness) offset from the preselected balance. This model canbe derived from a study of the printer exposure adjustment mechanisms.Digital transform 136 also provides for the incorporation of uniquereference identifiers (in the form of numbers 1 to 37, and letters Athrough H and N, as seen on FIG. 2) associated with each rendering onthe reference chart "Associated with" means it is apparent on theprinted image which identifier goes with which image. In the case ofreference chart 154, the unique identifier is printed as part of eachrendering (such as the unique identifier "1" shown in FIG. 2A). Digitalimage 138 represents represents the exposures that would be recorded ineach photosensitive layer of the product photographic paper at the timeof printing, for a preselected printer exposure or color balanceposition. The digital image 138 can be montaged (that is, integrated) ata preselected location into a larger digital image representing thewhole reference chart 154. Digital image 142 represents the image of thereference chart at various stages of completion, as the componentimages, 138, are integrated into it. Step 144 represents the creation ofa new digital transform 136 corresponding to a new printer exposure orcolor balance setting. When all of the component images of the referencechart have been created and integrated into the reference chart image,142, it is transformed by digital transform 146. Transform 146 convertsthe reference chart image into a metric suitable for a digitalopto-electronic film writer and provides for tone and color calibrationof the filmwriter. The digital filmwriter outputs the digital image ofthe reference chart, 148, producing a film negative 150 of the referencechart, 154. This negative 150 is on a film suitable for use in thedigital film writer and may be different from either the capture film orthe product film. Negative 150, however, prints in a single exposureonto the product paper, exactly (within the limits of modeling error) aswould a negative of the reference image, on the product film type,printed at the range of exposure and color balance settings representedon the reference chart. The negative of the reference chart is printedphotographically, 152, onto the product paper using a photographicprinter or enlarger resulting in the reference chart 154.

Reference chart 154 is a chart with 45 different renderings of the sameimage identified by the hexagons numbered with unique identifier numbers1 to 37, A to H, and N. Each rendering is different from otherrenderings by specific amounts of log exposure. The renderings of chart154 are preferably printed with the same colorants and on the samesubstrate 158 as will be used for making photographic prints of areference film strip 160 carrying unprocessed reference images. Moreparticularly, chart 154 is preferably formed by exposing and processing(that is, developing and fixing the image) the same type of photographicpaper as will be used for printing images from the reference film strip160 and from a customer film strip 170. The exposed and processed paperbecomes substrate 158 and the dyes in the paper become the imagecolorants. By the same "type" of a photographic medium (such as paper orfilm) is meant having the same photographic characteristics, andnormally references media manufactured in the same way with the samecomponents. Reference film strip 160 and customer film strip 170 aredescribed below in connection with FIG. 3. By using the same type ofphotographic media the color gamut, gloss, contrast, and white point ofthe printed reference images, reference chart, and printed customerimages, will be identical and an appearance match between the referenceimage and reference chart can be obtained regardless of viewingconditions.

The renderings are in two groups, with all the renderings preferablybeing on a gray background on substrate 158 to reduce chromaticinduction effects. A first group of renderings simulates equally spacedprinter exposures resulting in a range of lightness at a constant colorbalance. This first group is on the left side of chart 154, and varyfrom Lightest to Darkest, lettered from A to H (A being the lightest ofthe first group, that is the least exposure, and H being the darkest ofthe first group, that is the greatest exposure). These renderings areseparated by equal changes in log exposure, with D being the renderingrecommended by the manufacturer of the kit (hence D has what themanufacturer regards as the recommended density for this scene).

The second group, identified by numbers 1 to 37, on the right hand sideof chart 154, changes in color balance. The center patch 1 is therecommended color and density (identical to "D" from the left side).Adjacent renderings in a given direction on the chart preferablysimulate a constant log exposure difference, such as 0.030 relative logexposure. This difference preferably corresponds to the color correctionbutton increments commonly found on photofinishing optical printers.Thus, all the renderings immediately adjacent to and surrounding a givenrendering simulate a constant log exposure offset from that givenrendering but in different color directions. The different color balancerenderings are achieved by adjusting the relative log exposures in threecolor dimensions--the red/cyan, green/magenta and yellow/blue axes. Forexample, in order to make a rendering with a more yellow color balance,the yellow/blue exposure would be increased relative to the red/cyan andmagenta/green exposures. The changes to these exposures are made in away that maintains a constant level of lightness (relative brightness,independent of chromaticity) in the renderings. Lightness andchromaticity can be described, for example, using the CIE L*a*b* colorspace (see R. W. G. Hunt, The Reproduction of Color Fourth Edition,1987, Fountain Press, Tolworth, England).

Chart 154 also has a correctly exposed and color balanced rendering Nincluded on the plain gray background of the reference chart tofacilitate critical comparison without the distraction of surroundingimages. Rendering N is the same as D (which in turn is the same asrendering 1).

It will be appreciated that the log exposure differences betweenrenderings need not be maintained constant, but could be varied toassist in use of the chart with any image output device.

Referring to FIG. 3, an apparatus of the present invention and themethod of using it for calibrating a photographic printer, are shown.The apparatus is in the form of a kit, and includes reference chart 154,a reference film strip 160, a look up table 162, and an indication thatthe kit is to be used for establishing a printer calibration for anidentified film type or types. By a "kit" is meant that all of theelements of the apparatus are provided together (typically in a singlepackage). The foregoing indication may be in the form of printedinstructions associated with the kit (for example, instructions enclosedwith the kit or on its packaging) specifying that the kit is for printercalibration for the stated film type or types (preferably for a filmtype the same as that of the unprocessed reference film strip 160). Thekit may additionally comprise an indication that the photographic printsof the reference image are to be made on the same type of photographicmedium as the reference chart 154 was made. This indication may be inany of the forms of the previously mentioned indication.

Look up table 162 is shown in the form of the same unique identifiers onreference chart 154, printed in association with correspondingcorrection factors printed on a paper substrate which are the values forchanging the printer output to match a predefined aim rendering(rendering 1 or N, in FIG. 2). The kit enables calibration of theprinter for customer images made on the same type of film as thereference film strip. Reference film strip 160 carries latent images(that is, exposed but not processed) of a scene which is suitable forcalibrating a printer. This scene would typically contain neutral (thatis, one or more gray levels including black and white, which aresubstantially achromatic) and non-neutral color elements. Preferably thescene would contain multiple objects, and could be a real world scene orcomputer generated scene. Preferably the scene would include human skincolors and other common colors such as sky blue, green foliage, and thelike. Most preferably, the scene will be the same as that in therenderings carried by reference chart 154. Typically, the scene would beexposed onto the reference filmstrip at a number of different exposurelevels, providing at least one normally exposed latent image and one ormore latent images that are either under exposed or over exposed. Forexample a typical reference film strip may contain images exposednormally, 21/2 stops under exposed, 21/2 stops over exposed and 5 stopsover exposed. This facilitates calibration of the photographic printerfor negatives of different exposure levels as would typically beencountered in customer orders. Preferably the reference film strip 160is produced using second generation original methods similar to thosedescribed in U.S. Pat. Nos. 5,223,891 and 5,313,251.

Look up table 162 consists of one or more sets of printer adjustmentfactors corresponding to the differences between the various renderingsof the reference image (as identified by the unique identifiers) on thereference chart These adjustment factors correspond to changes in therelative exposure levels in the red/cyan, green/magenta or yellow/bluechannels of a photographic printer. By using these adjustment factorsthe photofinisher is able to change the appearance of prints produced byhis photographic printer from matching the density or color balance of aparticular rendering on the reference chart to matching the density orcolor balance of any other rendering on the reference chart.

The method of using the kit to calibrate a photographic printer beginswith processing of the reference film strip 160 in the film processor210 of the photofinishing system. The photofinishing system includes afilm processor 210, photographic optical printer 215, and paperprocessor 230 typically all located at the same single location. Anadvantage of processing the reference film strip at the photofinisher,rather than providing a fully processed film strip in the kit, is thatthis method accounts for biases that may be present in the filmprocessing operation of the particular photofinishing system. Theprinter calibration thus obtained will therefore be correct for printingnegatives produced using the film processor of the particularphotofinishing system rather than simply correct for an `ideallyprocessed` film negative. Processing the reference film strip in thefilm processor produces a strip of reference calibration negatives 212.The photofinisher then makes reference prints of the referencecalibration negatives 212 using the printer 215 of the photofinishingsystem. These prints will most preferably be made on the same type ofphotographic paper that the reference chart is printed on and thatcustomer prints are made on. The reference prints are processed in thepaper processor 230 of the photofinishing system. The reference prints220 are then compared to the reference image renderings on the referencechart 154. Preferably two comparisons are made--one based on imagedensity using the renderings A to H on the reference chart and the otherbased on color balance using the renderings 1 to 37 on the referencechart. This comparison is preferably made visually, but referenceneutral and/or color patches 156 can be included in the reference imageto enable comparison using a densitometer. The renderings on thereference chart that match (that is, appear visually to be most similar)the reference prints 220 most closely in density and color balance arenoted. The photofinisher also determines the aim reference rendering onthe reference chart. This aim is the rendering having the most desirablecolor balance and density in the opinion of the photofinisher. Typicallythe aim rendering recommended by the kit manufacturer, is clearlyidentified on the reference chart and is generally located in the centerof the color balance ring around (that is, rendering number 1 in FIG.2). If the reference images 220 match the aim rendering then the printeris calibrated. If the reference prints do not match the aim renderingthen lookup table 162 is used to determine the printer correctionfactors needed to obtain output from the printer matching the aimrendering. The printer correction factors so obtained are applied to theprinter and a new series of reference prints are made from the referencenegatives 212 and processed. These new reference prints are againcompared to the reference chart as described above. This cycle may berepeated as necessary until the reference prints match the aim renderingon the reference chart.

Once printer calibration is satisfactory customer films 170 of the sametype as the reference film strip 160 can be processed in film processor210 (under the same processing conditions as used for reference filmstrip 160) and printed using printer 215 onto the same type ofphotographic paper from which reference chart 154 is made. The printedcustomer images are then processed in print processor 230 (under thesame processing conditions as used for processing the reference prints).In this way, correctly exposed and color balanced customer prints willbe obtained.

Since the reference film strip 160 contains under and over exposedimages in addition to the normally exposed image, printer under and overslope calibrations can be established to optimally print under and overexposed customer negatives in addition to normally exposed customernegatives.

Various modifications can, of course, be made to the above embodiments.For example, look up table 162, rather than carrying the correctionfactors in a human readable form on a substrate, could carry thecorrection factors in the form of only machine readable data carried bya suitable substrate, such as a machine readable magnetic or opticalstorage medium (for example, a computer diskette) or solid state memory.Of course, the user at a photofinishing lab would need a suitable reader(such as a computer) for this data. The correction factors when in theform of machine readable data, may be just carried by the memory of acomputer contained as part of a computer controlled printer. This couldthereby allow such a computer controlled printer to determine thenecessary correction factor to be applied to a printer after the userhas made the visual comparison.

It will also be appreciated that the photographic prints output byprinter 215 need not be of the reflection kind (that is, they need notbe a photographic paper), but could be of the transparent kind forprojection or viewing by transmitted (rather than reflected) light.

The invention has been described with reference to a preferredembodiment However, it will be appreciated that variations andmodifications can be effected by a person of ordinary skill in the artwithout departing from the scope of the invention.

    ______________________________________                                        PARTS LIST                                                                    ______________________________________                                        1-37        Unique Idenfifier Numbers                                         102         Capture Film                                                      104         Sensitometer                                                      106         Sensitometer Exposure                                             108         Scene                                                             110         Original Image                                                    112         Fiim Processor                                                    114         Sensitometric Exposures                                           116         Digital Film Scanner                                              118         Digital Image                                                     120         Digital Data Transform                                            122         Digital Image                                                     124         Digital Transform                                                 126         Ditigal Image                                                     128         Second Transform                                                  130         Digital Image                                                     132         Digital Transform                                                 134         Digital Image                                                     136         Digital Transform                                                 138         Digital Image                                                     140         Steps                                                             142         Digital Image                                                     144         Step                                                              146         Digital Transform                                                 148         Reference Chart                                                   150         Negative                                                          152         Step                                                              154         Chart                                                             156         Reference Neutral and/or Color Patches                            158         Substrate                                                         160         Film Strip                                                        162         Look Up Table                                                     170         Customer Film Strip                                               210         Film Processor                                                    212         Reference Calibration Negatives                                   215         Printer                                                           220         Reference Prints                                                  230         Processor                                                         ______________________________________                                    

What is claimed is:
 1. A kit for calibrating a printer of aphotofinishing system, comprising:(a) a reference film strip carrying atleast one reference image; (b) a print having a reference chart, saidreference chart comprising multiple renderings of the reference imageexposures and which include an aim rendering, each rendering having aunique identifier; and (c) a substrate carrying a list of printercorrection factors associated with each of said unique identifiers, saidrenderings are used to visually match a print made from said referenceimage obtained from said reference film strip after development thereof,said unique identifier of the visually matched rendering is used to findthe associated correction factor on said substrate for correcting theset-up of said printer.
 2. A kit according to claim 1 wherein thereference film strip carries the reference image as a developed image.3. A kit according to claim 1 wherein the reference image containsneutral and non-neutral color information.
 4. A kit according to claim 1additionally comprising an indication that the kit is to be used forestablishing a printer calibration for an identified film type.
 5. A kitaccording to claim 1 wherein the reference chart carries the multiplerenderings on a photographic medium, the kit additionally comprising anindication that photographic prints of the reference image are to bemade on a same type of photographic medium as the reference chart.
 6. Akit according to claim 1 wherein the reference film strip is a secondgeneration original.
 7. A kit according to claim 1 wherein the referenceimage contains only neutral color information.
 8. A kit according toclaim 1 wherein the reference chart is produced on developed colorphotographic paper.
 9. A kit for calibrating a printer of aphotofinishing system, comprising:(a) an exposed and unprocessedreference film strip carrying at least one latent reference image; (b) aprint having a reference chart, said reference chart comprising multiplerenderings of the reference image exposures and which include an aimrendering, each rendering having a unique identifier; and (c) asubstrate carrying a list of printer correction factors associated witheach of said unique identifiers said renderings are used to visuallymatch a print made from said reference image obtained from saidreference film strip after development thereof said unique identifier ofthe visually matched rendering is used to find the associated correctionfactor on said substrate for correcting the set-up of said printer. 10.A kit according to claim 9 additionally comprising an indication thatthe kit is to be used for establishing a printer calibration for a filmtype the same as that of the unprocessed reference film strip.
 11. Amethod of calibrating a photofinishing system using a kit comprising:(a)a reference film strip carrying at least one reference image; (b) areference chart carrying multiple renderings of the reference imagerepresenting different printer exposures; and (c) a substrate carryingprinter correction factors needed to change a photographic printobtained from the reference image on the reference film strip, to matchany desired rendering on the reference chart; comprising the stepsof:(a) making a print of the at least one reference image from thereference film strip using a printer of the photofinishing system; (b)comparing the print resulting from step (a) with the multiple renderingson the reference chart, to find a matched rendering on the referencechart; (c) determining the printer correction factor from the factors onthe substrate corresponding to the matched rendering from step (b) andan aim rendering; and (d) adjusting the printer in accordance with theprinter correction factor identified in step (c).
 12. A method accordingto claim 11 wherein the reference chart is carried on a photographicmedium, and the print of the reference image is made on the same type ofphotographic medium on which the reference chart is carried.
 13. Amethod of calibrating a photofinishing system using a kit,comprising:(a) an exposed and unprocessed reference film strip carryingat least one latent reference image; (b) a print having a referencechart, said reference chart comprising multiple renderings of thereference image exposures and which include an aim rendering, eachrendering having a unique identifier; and (c) a substrate carrying alist of printer correction factors associated with each of said uniqueidentifiers, said renderings are used to visually match a print madefrom said reference image obtained from said reference film strip afterdevelopment thereof, said unique identifier of the visually matchedrendering is used to find the associated correction factor on saidsubstrate for correcting the set-up of said printer, comprising thesteps of:(a) developing the at least one latent reference image on thereference film strip, in a film developing process of the photofinishingsystem; (b) making a print of a developed reference image from step (a)using a printer of the photofinishing system; (c) comparing the printresulting from step (b) with the multiple renderings on the referencechart, to find a matched rendering on the reference chart; (d)determining a printer correction factor from a factor on the substratecorresponding to the matched rendering from step (c) and an aimrendering; and (e) adjusting the printer in accordance with the printercorrection factor identified in step (d).
 14. A method according toclaim 13 additionally comprising developing further latent images on asame film type as the reference film strip using a same film developingprocess of the photofinishing system, and printing the developed furtherlatent images on a same printer of the photofinishing system afteradjusting the printer according to step (e).